There is some evidence that points to a hybridization event between Au. afarensis and gorilla ancestors around 3 million years ago. Based on that, the idea is that Paranthropus, as a form of hybrid species, was adopted by early Homo as a companion species, which formed conditions where (rudimentary) eusociality could evolve.
Eusociality may be limited by that a species shares the same gene pool, so it is difficult to get “labour dimorphism” and division of labour. Technology of course extends the phenotype beyond the gene pool, but at an early stage perhaps a two-species scenario could explain some things, and form rudimentary adaptations that were later on co-opted, through technology and more advanced memetic evolution, for even more eusociality.
The partner-species phase could solve a “chicken or the egg” problem.
What is the “companion-species hypothesis”?
A very far out idea, based around Edward O'Wilsons notion that humans are a "eusocial species of ape". Eusociality is defined as having a caste system, and a division of labour, and humans are the only mammal that are eusocial. The rudimentary traits for eusociality could possibly have evolved from two species co-existing, and then later on have been co-opted for other things. It may sound absurd, but the human species is unlike any other animal on the planet, and so our evolutionary history may well be an unusual one.
"Co-existing with a less intelligent species, Paranthropus, could be a breeding ground for machiavellian intelligence, as they would have been more easily manipulated, as well as for breeding traits necessary for a caste based societal system which is the definition of eusocial organization (eusociality, wikipedia). "
Below is an artist depiction of a Paranthropus bosei, via https://sci-news.com/othersciences/anthropology/science-homo-pan-last-common-ancestor-03220.html
